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* *Reflection: Rigor
Line Segments - Section 2: Direct Instruction

In this age of texting and tweeting, it seems that it's becoming harder to get students to be precise with their use and interpretation of mathematical notation. In this lesson, students must distinguish between the notation for line AB, line segment AB, and length of line segment AB.

Having just completed the school year, I have to say that a significant portion of my honors students were still not clear on these distinctions. In some cases, it was a matter of neglect, but in other cases, students really just didn't know. On the final exam, I still had students asking me "Does this say segment or the length of the segment?" and many students failed to use correct notation in their work.

I stressed precision continually this year, but I did not really penalize students for being imprecise. If I had it to do over again, I would be very hard on students at the beginning, taking points of for using imprecise notation. That way, students would develop the habits early on and maintain them throughout the year. I had hoped that my constant harping would do the trick, but this experience taught me that sometimes students (at least mine) need to see a direct correlation between a desired behavior and their grades.

*Demanding precision from the start*

*Rigor: Demanding precision from the start*

# Line Segments

Lesson 2 of 14

## Objective: SWBAT create and interpret geometric notation and diagrams involving line segments and their measures; SWBAT measure line segments and construct line segments to specifications

#### Measurement and Construction

*20 min*

An overarching goal for this course is to impress upon students that, while Geometry is a very abstract subject, we have tools that allow us to make very concrete measurements involving geometric concepts. In this section of the lesson, students learn to use a ruler to measure segments. In my experience, it is a mistake to assume that students already know how to do this.

I start with an introduction to the markings on the ruler. I start with the metric side of the ruler since it is somewhat easier to understand for a novice. Next I model measuring lengths using a ruler. I do this on the document camera so that students can see clearly what I am doing.

Next I hand out the resource: Measuring and Creating Segments. As students work on the exercise, I circulate around the room playing the role of questioner/facilitator.

The types of questions I ask:

1. What do the directions say?

2. What information is given here?

3. Have you been as precise as possible in making your measurement?

4. How could you express in geometric notation that the length of the segment is.............cm?

#### Resources

*expand content*

- UNIT 1: Community Building, Norms, and Expectations
- UNIT 2: Geometry Foundations
- UNIT 3: Developing Logic and Proof
- UNIT 4: Defining Transformations
- UNIT 5: Quadrilaterals
- UNIT 6: Similarity
- UNIT 7: Right Triangles and Trigonometry
- UNIT 8: Circles
- UNIT 9: Analytic Geometry
- UNIT 10: Areas of Plane Figures
- UNIT 11: Measurement and Dimension
- UNIT 12: Unit Circle Trigonmetry
- UNIT 13: Extras

- LESSON 1: Origins of the Geometric Universe
- LESSON 2: Line Segments
- LESSON 3: Distances in the Coordinate Plane
- LESSON 4: Exploring Midpoint Quadrilaterals
- LESSON 5: Investigating Points, Segments, Rays, and Lines
- LESSON 6: Formative Assessment Day 1
- LESSON 7: Introducing Angles
- LESSON 8: Angle Measurements
- LESSON 9: Basic Constructions
- LESSON 10: Measuring to find Perimeter and Area
- LESSON 11: Finding Perimeter and Area in the Coordinate Plane
- LESSON 12: Geometry Foundations Summative Assessment Practice Day 1 of 2
- LESSON 13: Geometry Foundations Summative Assessment Practice Day 2 of 2
- LESSON 14: Introduction to Transformations